Quick facts:

Humanity’s impact on the environment is a product of our population and our environmental footprint per person. Our footprint is, in turn, a product of our consumption pattern (affluence) and the way we achieve it (technologies, behaviours and institutions). This is often summarised in the “IPAT” equation:
I = P x A x T (Impact = Population x Affluence x Technology)

Humanity’s impacts on the biosphere are now so profound that geologists have labelled the current period the “Anthropocene”, meaning the era shaped by humans.

Global warming is one feature of the Anthropocene. Others include species extinctions, persistent pollutants, loss of forests and other natural habitats, soil erosion, freshwater diversions, ocean acidification and overloading the environment with nitrogen and phosphorus.

We are in the middle of the planet’s sixth great extinction event, in which the number of species on earth is greatly reduced. Species extinctions are now happening many times faster than they were over thousands of years before the industrial revolution. Humans are the cause.

While some of the impacts of the richest billion people are avoidable (either frivolous or wasteful), the poorest half of humanity need more access to the resources of nature in order to attain a reasonable quality of life. The quality of life they will be able to achieve depends greatly on how many people there will be.

“Carrying capacity” is the number of people who can live, in the way they happen to be living, without damaging the environment or diminishing its ability to support people in the future.

Humanity has been exceeding the sustainable carrying capacity of the Earth since 1981, according to the Global Footprint Network.

We can increase (and have greatly increased) the planet’s carrying capacity by doing things in less impactful ways. But population growth undoes all the efforts we make to have less impact per person, or to deliver better access to food, water, energy and services per person.

The lower the peak global population, the more likely that humanity can achieve a peaceful and sustainable future.